[Discuss-gnuradio] usrp A/D scaling question

[John DuBois]

I am puzzled by a very basic issue relating to the usrp1 output. Using 
GRC, I connect the usrp output through a complex to mag conversion to a 
scope sink and tune to, say, 1GHz. The daughter board is a DBS_RX.

Using a cw signal generator, I tune for a maximum usrp output and then 
raise the usrp input  up to about -45 dBm. As the input increases, I see 
rising output values (on the scope display) from just above zero to a 
maximum of about 16400.

The puzzle is this: if the usrp A/D converter is 12 bits for I and Q 
channels and I am doing a complex to magnitude conversion, why don't I 
see 4095*1.414 as the maximum output number?

The maximum output I do see seems like 14 bits, but without any 1.414 
factor.

What am I missing ??